Organic polyisocyanate-dialkyl carbonate adhesive binder compositions

ABSTRACT

An adhesive binder composition is provided for the preparation of lignocellulosic composite molded articles such as flake or particle board, made from moldable compositions which comprises an organic di- or polyisocyanate and a liquid dialkyl ester of carbonic acid and optionally lignin, for application to the lignocellulosic material prior to the molding process to form the composite product.

FIELD OF THE INVENTION

The present invention relates generally to the compression molding oflignocellulosic materials into composite bodies, sheets and the like andmore particularly to an organic di- or polyisocyanate based bindersystem for the lignocellulosic material which imparts equivalent orimproved properties to the molded pressed composite product atsubstantially reduced isocyanate binder levels.

BACKGROUND OF THE INVENTION

The molding of lignocellulosic and lignocellulosic-containing fibers,particles or layers to form composite articles is known. The binderswhich normally are used are the synthetic resin glues such as a solutionof urea-formaldehyde or phenol-formaldehyde resin in water. Compositeproducts containing lignocellulose produced in this way lack durabilityand are susceptible to moisture conditions and deterioration in certainbuilding purposes to which they may be subjected.

Di- and polyisocyanates as binders for lignocellulose materials havebeen proposed and are known to give products of increased stability andmechanical strength. Process technical advantages of polyisocyanateshave been disclosed in German Offenlegungsschrift No. 2,109,686. Twoproblems associated with the use of polyisocyanate binders are (1) evenat reduced binder use levels, the cost of the polyisocyanates ascompared to the ureaformaldehyde or phenol-formaldehyde resin binders isunfavorable and (2) the viscosity of the normally employedpolyisocyanate binders are much higher than the synthetic glue resinsand are therefore difficult to apply to the lignocellulose with currentapplication equipment or methods. The advent of technology to emulsifythe polyisocyanates in water provided a binder product with reducedviscosity but with a service life of only 2 to 4 hours.

The present invention which comprises an improved polyisocyanate basedadhesive binder composition that has been extended through the additionof a liquid dialkyl esters of carbonic acid and optionally lignin,avoids the above mentioned disadvantages.

SUMMARY OF THE INVENTION

This invention relates to the preparation of a polyisocyanate-liquiddialkyl carbonate binder composition and its use for the preparation oflignocellulosic composite molded products.

It is the principal object of this invention to provide an improvedlignocellulosic binder and composition which gives properties equivalentto or better than prior molded pressed composite products atdramatically reduced di- or poly-isocyanate (referred to generally aspolyisocyanates) levels and cost.

The advantages of the present invention is that the levels of the di- orpoly-isocyanate necessary to produce a cured pressed compositelignocellulosic product can be substantially reduced while maintainingequivalent or superior composite board physical properties. By employingthe di- or polyisocyanate-dialkyl carbonate combination, with or withoutthe use of lignin as a diluent, the binder resin economics areequivalent or better than the synthetic glue resin economics. Thecomposite products made with the adhesive binders of the presentinvention have superior physical properties to those prepared with theurea-formaldehyde or phenol-formaldehyde binder systems. The addition ofthe liquid dialkyl carbonates (dialkyl esters of carbonic acid) to thedi- or polyisocyanates reduces the overall viscosity of the bindersystem while exhibiting a marked increase in service life of up tothirty (30) days. The binder system of the present invention hasviscosities equivalent to or lower than the formaldehyde type resinsystems in water, which allows the instant binder system to be appliedto the lignocellulosic chips, particles, etc., using present applicationtechnology. As a further advantage, the binder system of the presentinvention can be employed with high molecular weight solid or semisoliddi- or polyisocyanates which by themselves would have properties whichwould preclude their use as adhesives for lignocellulosic products withcurrent application techniques.

DESCRIPTION OF THE INVENTION

In accordance with the present invention an adhesive binder compositioncomprising a dialkyl carbonate having from 3 to 11 carbon atoms ormixtures thereof and an organic di- or polyisocyanate, with or withoutthe addition of lignin, is provided for the preparation oflignocellulosic composite bodies or sheets which comprises shaping in amold or between mold surfaces in the form of a caul plate or platen amixture of the lignocellulosic material and the isocyanate based binderof the present invention generally at temperatures of from about 140° C.to 220° C., preferably 160° C. to 190° C., at pressures of from about100 to 600 psi for a period of from 1 to 10 preferably 3 to 5 minutes,there being provided at the interface of the mixture and mold surface orsurfaces a release agent such as a metallic soap.

The organic polyisocyanates are generally applicable as binders in thepresent invention. Organic polyisocyanates which may be used includealiphatic, alicyclic and aromatic polyisocyanates characterized bycontaining two or more isocyanate groups. Such polyisocyanates includethe diisocyanates and higher functionality isocyanate, particularly thearomatic polyisocyanates. Mixtures of polyisocyanates may be used whichfor example are the crude mixtures of di- and higher functionalitypolyisocyanates produced by phosgenation of aniline-formaldehydecondensates or as prepared by the thermal decomposition of thecorresponding carbamates dissolved in a suitable solvent as described inU.S. Pat. Nos. 3,962,302 and 3,919,279 both known as crude MDI or PMDI.The organic polyisocyanate may be isocyanate-ended prepolymers made byreacting under standard known conditions, an excess of a polyisocyanatewith a polyol which on a polyisocyanate to polyol basis may range fromabout 20:1 to 2:1 and include for example polyethylene glycol,polypropylene glycol, diethylene glycol monobutyl ether, ethylene glycolmonoethyl ether, triethylene glycol, etc. as well as glycols orpolyglycols partially esterfied with carboxylic acids includingpolyester polyols and polyether polyols. The organic polyisocyanates orisocyanate terminated prepolymer may also be used in the form of anaqueous emulsion by mixing such materials with water in the presence ofan emulsifying agent. The isocyanates may also contain impurities oradditives such as carbodiimides, isocyanurate groups, urea, hydrolyzablechlorides and biurets as well as certain release agents. Illustrative ofsuch di- or polyisocyanates which may be employed include, for example,toluene-2,4- and 2,6-diisocyanates or mixtures thereof,diphenylmethane-4,4'-diisocyanate (a solid) anddiphenylmethane-2,4'-diisocyanate (a solid) or mixtures of same, i.e.,containing about 10 parts by weight 2,4'- or higher, which are liquid atroom temperature, polymethylene polyphenyl isocyanates,naphthalene-1,5-diisocyanate, 3,3'-dimethyldiphenylmethane4,4'-diisocyanate, triphenylmethane triisocyanate,hexamethylene diisocyanate, 3,3'-ditolylene-4,4-diisocyanate, butylene1,4-diisocyanate, octylene-1,8-diisocyanate, 4-chloro-1,3-phenylenediisocyanate, 1,4- 1,3- and 1,2-cyclohexylene diisocyanates and ingeneral the polyisocyanates disclosed in U.S. Pat. No. 3,577,358. Thepreferred polyisocyanates are the diphenylmethane diisocyanate 2,4'and4,4'isomers including the 2,2'isomer and the higher functionalpolyisocanate and polymethylene polyphenyl isocyanate mixtures, whichmay contain from about 20 to 85 weight percent of the diphenylmethanediisocyanate isomers. Typical of the preferred polyisocyanates are thosesold commercially as "Rubinate-M" (Rubicon Chemicals Inc.) and "Papi"(Yhe Upjohn Co.). In general the organic polyisocyanates will have amolecular weight in the range between about 100 and 10,000 and will beemployed in amounts of from about 20 to 95 parts by weight, preferably50 to 75 parts by weight based on the polyisocyanatecarbonate mixture.

The liquid dialkyl esters of carbonic acid (dialkyl carbonates) ormixtures thereof employed in the present invention in amounts of fromabout 5 to 80 preferably 50 to 25 parts by weight based on theisocyanate-carbonate binder mixture contain from 3 to 11 carbon atomsand include, for example dimethyl, diethyl, di-n-propyl, diisopropyl,di-n-butyl, diisobutyl and diisoamyl carbonates as well as methyl ethylcarbonate, diallyl carbonate, methyl-n-propyl carbonate, ethyl-n-butylcarbonate, ethyl isopropenyl carbonate, ethyl n-propyl carbonate, etc.

As indicated hereinabove the addition of the dialkyl carbonate reducesthe overall viscosity of the binder system providing ease ofapplication. Typical of the viscosities attained in centipoise, (c.p.)at 25° C. are as follows using a diphenylmethanediisocyanatepolymethylene polyphenyl isocyanate mixture, soldcommercially as "Rubinate-M" by Rubicon Chemicals Inc. and having aviscosity of 230 c.p. at 25° C. Viscosities in centipoise was determimedafter aging 1, 7, 12 and 28 days at various ratios by weight ofpolyisocyanate to dialkyl carbonate.

    ______________________________________                                        230 c.p.         Centipoise After                                             Isocyanate       1 day     7 days                                                                              12 days 28 days                              ______________________________________                                                 Di-                                                                           Methyl                                                                        Car-                                                                          bonate                                                               3.0      0.5     16.2      16.2  16.8    17.1                                 2.5      1.0     4.9       4.9   5.2     6.1                                  2.0      1.5     1.4       1.5   1.8     1.9                                           Di-                                                                           Ethyl                                                                         Car-                                                                          bonate                                                               3.0      0.5     18.6      18.6  18.9    19.4                                 2.5      1.0     10.5      10.6  11.8    12.1                                 2.0      1.5     8.5       9.0   9.1     10.0                                          Di-                                                                           Allyl                                                                         Car-                                                                          bonate                                                               3.0      0.5     19.1      20.0  20.9    21.4                                 2.5      1.0     10.6      10.8  11.2    12.0                                 2.0      1.5     5.8       5.8   6.6     7.1                                  ______________________________________                                    

In addition a solid diphenylmethane-4,4'-diisocyanate was mixed withdimethyl carbonate at a parts by weight ratio of the 4,4'isomer todimethyl carbonate of 2.5:1.0, 2.0:1.5 and 3.0:0.5 and gave a mixturewith less than 60 c.p., a clear liquid mixture of 20 c.p. and a liquidmixture of less than 100 c.p. respectively.

The lignin which may be employed as a diluent in the binder system ofthe present invention are used in amounts of from 0 to 60 weightpercent, preferably from 20 to 35 weight percent based on the totalpolyisocyanate-dialkyl carbonate-lignin mixture. The exact compositionof lignin varies. Lignin derived from a variety of sources may be usedin the binder system of the present invention to form the adhesivemixture. One source is a mixture of waste liquors resulting from thechemical pulping of lignocellulose. Suitable lignin which may beemployed include, for example, purified pine wood lignin, kraft wasteliquior, soda waste liquor, calcium, magnesium, sodium and ammonium basesulfite liquors, chlorinated waste liquors, etc. Lignins from hardwoodand softwood sources may be used as well as lignins fromacid-precipitated and alkali-reconstituted kraft liquors. The abundantand available chlorinated waste liquors derived from paper mill bleachmay be used. The waste liquors may be used in their original conditionsin the adhesive binder composition of the instant invention. The ligninmay also have a wide range of pH and a solids content of from about 10to 90 weight percent. When employed, the lignin is simply physicallymixed with the isocyanate-carbonate adhesive when prepared or applieddirectly to the lignocellulosic material.

Lignocellulose, according to the present invention, used to prepare thelignocellulosic-containing composite articles include wood chips, woodfibers, shavings, sawdust, wood wool, cork, bark and the like productsfrom the wood-working industry. Fibers, particles, etc. from othernatural products which are lignocellulosic such as straw, flax residues,dried weeds and grasses, nut shells, hulls from cereal crops such asrice and oats and the like may be used. In addition, the lignocellulosicmaterials may be mixed with inorganic flakes or fibrous material such asglass fibers or wool, mica and asbestos as well as with rubber andplastic materials in particulate form. The lignocellulose may contain amoisture (water) contentof up to about 25 percent by weight butpreferably contains between 4 and 12 percent by weight.

In manufacturing lignocellulosic composite products for the purpose ofthis invention, such as flakeboard for example, a small amount of thebinder (with or without lignin) along with the lignocellulosic materialis simply milled or mixed uniformly together. Generally theisocyanate-dialkylcarbonate binding agent (with or without lignin) issprayed onto the material while it is being mixed or agitated insuitable and conventional equipment. Various type mixing equipment suchas an intensive shear mixer may be employed. The binder use levelsaccording to the present invention, based on the weight of oven dried(0% moisture content) lignocellulosic material is from about 1.5 to 12preferably 2.5 to 6.5 weight percent. The lignocellulose-adhesive bindermixture is generally sprinkled or formed in the desired proportions ontoa caul plate of aluminum or steel which serves to carry the "cake" intothe press to give the desired thickness of product, the plates havingbeen sprayed or coated with a release agent such as the metal soaps likethe iron, calcium or zinc stearate compounds. Other conventional releaseagents such as sodium phenolate and certain tertiary amines may also beemployed.

The following examples are provided to illustrate the invention inaccordance with the principles of this invention but are not to beconstrued as limiting the invention in any way except as indicated bythe appended claims.

In the Examples which follow, the test results set forth are expressedas ASTM D 1037 values and wherein

    ______________________________________                                        M.C.         is Moisture Content (%)                                          I.B.         is Internal Bond (psi)                                           T.S.         is cold water (25° C.) thickness                                       swell, 24 hr. immersion (%)                                      PMDI         is a mixture of liquid diphenyl-                                              methane diisocyanate-polymethylene                                            polyphenyl isocyanate having a                                                46.5% diphenylmethane diisocyanate                                            content                                                          DMC          is dimethyl carbonate                                            DEC          is diethyl carbonate                                             DAC          is diallyl carbonate                                             DIBC         is diisobutyl carbonate                                          TDI          is toluene-2,4-diisocyanate                                      TPMI         is triphenylmethane triisocyanate                                ______________________________________                                    

EXAMPLE 1

580 g. of pine wood chips dried to a moisture content of 6 percent areplaced in an open tumbler-mixer. During tumbling, 3.5 parts based on 100parts by weight of the wood of an isocyanate based binding agentprepared by mixing 70 parts crude liquid diphenylmethanediisocyanate-polymethylene polyphenyl isocyanate (PMDI) mixture having46.5 percent diphenylmethane diisocyanate content and 30 parts dimethylcarbonate are sprayed over the chips by an air pressurized system. Twocaul plates 12 inches square are sprayed evenly with a zinc stearateexternal release agent. Using a former box, a 10.5 inch square "cake" ofthe chip-binder mixture is formed on the caul plate. The second caulplate is placed over the cake which is pressed to stops at a thicknessof 13 mm at 190° C. for 41/2 minutes after which the pressed cake isreleased from between the press plates and cut into specimens forphysical testing. Test results of the composite board is 143 psi I.B.and a T.S of 19.3 percent.

EXAMPLES 2 to 5

The procedure of Example 1 is repeated exceptthat different levels ofdimethyl carbonate are substituted with crude liquid diphenylmethanediisocyanate-polymethylene polyphpenyl isocyanate (PMDI) mixture having46.5 percent diphenylmethane diisocyanate content while maintaining thetotal binder level constant at 3.5 percent based on 100 parts by weightof the wood.

                  TABLE I                                                         ______________________________________                                        Ex.       PMDI    DMC         I.B. T.S.                                       No.       (%)     (%)         (psi)                                                                              (%)                                        ______________________________________                                        2         85      15          153  15                                         3         78      22          130  21                                         4         43      57          123  28                                         5         100      0          165  18                                         ______________________________________                                    

EXAMPLES 6 to 9

The procedure of Examples 1 to 5 is repeated except with the followingchanges. The total binder level is held constant at 4.5 percent based on100 parts by weight of the wood. A third component, lignin, a productresulting from the chemical pulping of lignocellulose, is added to thebinder mixture. The liquid diphenylmethane diisocyanate-polymethylenepolyphenyl isocyanate (PMDI) mixture having a 46.5 percentdiphenylmethane diisocyanate content and dimethyl carbonate contentvaries over the range specified in Table 2.

                  TABLE 2                                                         ______________________________________                                        Ex.  PMDI       Lignin  DMC       I.B. T.S.                                   No.  (%)        (%)     (%)       (psi)                                                                              (%)                                    ______________________________________                                        6    66.8       22.2    11.0      138  24                                     7    61.0       22.2    16.8      135  23                                     8    55.5       22.2    22.3      129  25                                     9    44.4       22.2    33.4      130  26                                     ______________________________________                                    

EXAMPLES 10 to 14

The procedure for Examples 1 to 9 are repeated except for the followingchanges: diethyl carbonate is substituted for dimethyl carbonate. Thebinder level for 10 to 13 is held constant at 3.5 percent based on 100parts by weight of the wood. Example 14 includes 22 weight percentlignin with a 4.5 weight percent binder level. The liquiddiphenylmethane diisocyanate-polymethylene polyphenyl isocyanate (PMDI)mixture having 46.5 percent diphenylmethane diisocyanate content andcarbonate percentages are varied according to Table 3 below.

                  TABLE 3                                                         ______________________________________                                        Ex.       PMDI    DEC         I.B. T.S.                                       No.       (%)     (%)         (psi)                                                                              (%)                                        ______________________________________                                        10        100.0   --          165  20                                         11        78.5    21.5        155  26                                         12        71.0    29.0        135  27                                         13        57.0    43.0        114  30                                         14        56.0    22.0        118  27                                         ______________________________________                                    

EXAMPLE 15 (COMPARATIVE)

The procedure for Examples 1 to 14 are repeated except phenolformaldehyde resin (6 percent) is used as the binder and the pressingtime is 9 minutes and pressing temperature 220° C. The following are thetest results which indicate that a wax must be added to the materialpressed to give desired properties.

    ______________________________________                                                I.B. T.S.                                                                     (psi)                                                                              (%)                                                              ______________________________________                                                101  32.3                                                             ______________________________________                                    

EXAMPLES 16 to 25

A number of runs are made in accordance with the procedure of Examples 1to 5, utilizing various dialkyl carbonates and isocyanate compositions.The binding agent was prepared by mixing 70 parts isocayante and 30parts carbonate. The binder level is maintained at 3.5 weight percentbased on 100 parts by weight of the wood. Example 25 is a mixture of 15parts DEC and 15 parts by weight of DAC. The carbonate and isocyanateswith test results are set forth in Table 4.

                  TABLE 4                                                         ______________________________________                                                            Poly-                                                     Ex.     Dialkyl     Iso-       I.B. T.S.                                      No.     Carbonate   cyanate    (psi)                                                                              (%)                                       ______________________________________                                        16      DMC         PMDI       148  20.3                                      17      DMC         TDI        128  25.2                                      18      DEC         TDI        126  25.0                                      19      DEC         TPMI       139  22.3                                      20      DAC         PMDI       140  20.5                                      21      DAC         TPMI       136  23.5                                      22      DIBC        TDI        118  24.0                                      23      DIBC        TPMI       132  21.6                                      24      DAC         TDI        135  21.9                                      25      DEC &       PMDI       150  21.0                                              DAC                                                                   ______________________________________                                    

We claim:
 1. An adhesive binder composition for the preparation ofcompression moldable lignocellulosic articles which comprises from about20 to 95 percent by weight of an organic di- or polyisocyanate and fromabout 5 to 80 percent by weight of a liquid dialkyl carbonate havingfrom 3 to 11 carbon atoms.
 2. The adhesive composition of claim 1wherein from 0 to 60 weight percent lignin based on the totalcomposition is added as diluent.
 3. The adhesive composition of claim 2wherein between 20 and 35 weight percent lignin is added as diluent. 4.The adhesive composition of claim 1 wherein the dialkyl carbonate isselected from the group consisting of dimethyl carbonate, diethylcarbonate, diallyl carbonate and diisobutyl carbonate.
 5. The adhesivecomposition of claim 4 wherein the dialkyl carbonate is dimethylcarbonate.
 6. The adhesive composition of claim 4 wherein the dialkylcarbonate is diethyl carbonate.
 7. The adhesive composition of claim 4wherein the dialkyl carbonate is diallyl carbonate.
 8. The adhesivecomposition of claim 1 wherein the di- or polyisocyanate is adiphenylmethane diisocyanate.
 9. The adhesive composition of claim 1wherein the di- or polyisocyanate is a mixture of diphenylmethanediisocyanate and the higher functionality polymethylene polyphenylisocyanates.
 10. The adhesive composition of claim 1 wherein from 50 to75 weight percent organic di- or polyisocyanate and from 50 to 25 weightpercent dialkyl carbonate is employed.
 11. A compression moldablelignocellulosic composition comprising lignocellulosic particles andfrom about 1.5 to 12 percent by weight based on oven dried particles ofan adhesive binder composition which comprises from about 20 to 95weight percent organic di- or polyisocyanate and from about 5 to 80weight percent liquid dialkyl carbonate having from 3 to 11 carbonatoms.
 12. The compression moldable composition of claim 11 wherein 2.5to 6.5 weight percent adhesive binder is employed in the composition.13. The compresson moldable composition of claim 11 wherein from 0 to 60weight percent lignin based on the total adhesive binder composition isadded as diluent.
 14. The compression moldable composition of claim 13wherein the lignin is between 20 and 35 weight percent.
 15. Thecompression moldable composition of claim 11 wherein the dialkylcarbonate is selected from the group consisting of dimethyl carbonate,diethyl carbonate, diallyl carbonate and diisobutyl carbonate.
 16. Thecompression moldable composition of claim 15 wherein the dialkylcarbonate is dimethyl carbonate.
 17. The compression moldablecomposition of claim 15 wherein the dialkyl carbonate is diethylcarbonate.
 18. The compression moldable composition of claim 15 whereinthe dialkyl carbonate is diallyl carbonate.
 19. The compression moldablecomposition of claim 11 wherein from 50 to 75 weight percent organicdi-or polyisocyanate and from 50 to 25 weight percent liwquid dialkylcarbonate is employed in the adhesive binder.
 20. The compressionmoldable composition of claim 11 wherein the di- or polyisocyanate is adiphenylmethane diisocyanate.
 21. The compression moldable compositionof claim 11 wherein the di- or polyisocyanate is a mixture ofdiphenylmethane diisocyanate and the higher functionality polymethylenepolyphenyl isocyanates.
 22. A composition board product comprising acompression molded lignocellulosic composition comprisinglignocellulosic particles and from about 1.5 to 12weight percent basedon oven dried lignocellulosic particles employed of an adhesive bindercomposition, said binder composition being a mixture of from about 20 to95 weight percent organic di- or polyisocyanate and from 5 to 80 weightpercent liquid dialkyl carbonate having from 3 to 11 carbon atoms. 23.The composition board product of claim 22 wherein from 0 to 60 weightpercent lignin based on the total adhesive binder composition is addedas diluent.
 24. The board product of claim 22 wherein the compressionmolded lignocellulosic composition is wood particle board.
 25. A methodfor the preparation of lignocellulosic composite articles comprising thesteps of(a) mixing together lignocellulosic particles and from about 1.5to 12 weight percent based on oven dried lignocellulosic particles of anadhesive binder composition comprising from 20 to 95 weight percentorganic di-and polyisocyanate and from about 5 to 80 weight percentliquid dialkyl carbonate having from 3 to 11 carbon atoms to form amoldable composition; (b) introducing said moldable composition onto ametal mold, caul plate or platen which has been sprayed or coated with arelease agent; (c) compression shaping said composition at temperaturesof between about 140° C. to 220° C. at pressures of from about 100 to600 psi for a period of from 1 to 10 minutes to form a composite articleof desired shape and/or thickness; and (d) thereafter releasing saidlignocellulosic composite article from said metal mold, caul plate orplaten.
 26. A method according to claim 25 wherein 2.5 to 6.5 weightpercent adhesive binder composition is employed and comprises from 50 to75 weight percent organic di-or polyisocyanates and from 50 to 25 weightpercent carbonate, the release agent is a metallic soap, the compressiontemperature is between 160° C. to 190° C. and the time period is from 3to 5 minutes.
 27. A method according to claim 25 wherein the bindercomposition is a mixture of diphenylmethane diisocyanate and the higherfunctionality polymethylene polyphenyl isocyanates and diethylcarbonate.
 28. A method according to claim 25 wherein the compressionmolded lignocellulosic composition is wood particle board.